Analog measurements of currents and voltages are typically very time consuming and can only be done on a small sample of electronic parts (or semiconductor devices). Generally, high cost probes and measuring equipment are needed to measure these analog currents and voltages on the semiconductor devices. These analog properties, such as bias voltage in an analog operational amplifier (OPAMP), current in a current mirror, gain of an OPAMP, bandwidth of an amplifier or comparator, output voltage swing of an input-output (I/O) buffer, etc., can be measured by pulling the respective nodes associated with the above analog properties to the highest metal layer of the semiconductor process for accessing the nodes via high cost probes. Analog nodes may also be accessed from the lowest metal layer of the semiconductor device through pico-probing where the substrate is thinned and a hole dug in the region of interest. Generally, analog properties are sensitive to many factors including temperature, voltage, process, impedance of the probes that touch the nodes associated with the analog properties, etc. This sensitivity makes it challenging to measure or monitor analog properties for any given part.
Moreover, for high volume manufacturing (HVM) of semiconductor processors (or devices) a large number of measurements is required for characterizing the processors. As analog properties of analog circuits become critical due to their sensitivities to various factors, HVM becomes challenging because processors vary in their performance due to within-die variations and across-die variations in the analog properties. Additionally, measuring and/or analyzing the analog properties for a smaller, yet statistically significant, number of processors on a wafer, and also measuring and/or analyzing the analog properties of a die (processor) on a wafer, is helpful to characterize the behavior of the analog circuits and thus to characterize the process files used in simulating such analog circuits before they are manufactured in high volume.
For example, output signal swings of an input-output (I/O) buffer of a processor represent an important analog property to characterize several I/Os of the processor on a wafer and to characterize several I/Os of other processors of the same wafer or different wafer. The output signal swing of an I/O buffer generally has tight electrical specifications which are met by careful design of analog circuits associated with the I/O buffer. A slight variation in the behavior of the analog circuits (for example, change in bias voltage level, bias current level, output impedance, etc.) associated with the I/O buffer may cause the output signal swing to violate its tight electrical specification. To design a robust I/O buffer, which can sustain variations in the behavior of the analog circuits associated with the I/O buffer, a well modeled simulation process file is helpful.